(PUP-3642) Remove environment name from URL path

This commit makes some changes to the indirector network layer
such that the environment name is no longer a part of the main
URL path structure.  This will allow us to have a more finite URL space
and run Puppet in the same webserver with other apps, without
worrying about URL collisions.  Instead, the environment becomes a query
parameter.
Yeah, it does seem a little weird to me too, but I think that the spirit of what @joshcooper and @Iristyle were suggesting is that it's OK to have params in both places on a single request, and that in this case it makes things a little more consistent/predictable for us because we will know that the environment is *always* in the query string, no matter what type of request we're using.  Putting it in the body for POSTs would work but we'd still have the same issue for PUT requests, which would take us back to that whole indirector model madness that started all of this :)